U.S. Pat. No. 3,905,888 discloses an electrochemical sensor for the in vivo determination of oxygen partial pressure in biological media, particularly blood.
Methods for the continuous measurement of oxygen partial pressure are known in the art for patients under intensive care treatment for various conditions of respiratory and cardiovascular failure, including hypoperfusion and vasoconstriction. A clinically practical and technically fully-developed blood gas measuring sensor is available as the Continucath 1000.TM. system manufactured and marketed by Biomedical Sensors Ltd. of High Wycombe, England.
The system includes an electrochemical sensor contained within a catheter having a wall of oxygen-permeable polymeric material which acts as a diffusion membrane. The structure of the sensor is similar to, but an improvement on, the structure of the sensor disclosed in U.S. Pat. No. 3,905,888. The distal end of the catheter is adapted to be inserted in a patient's artery, usually in the arm, and the system is activated immediately following connection of the proximal end of the catheter, via a suitable electrical connector, to a monitor.
The system provides continuous monitoring of intravascular pO.sub.2 and is an effective indicator of hypoxic and hyperoxic conditions.
Systems have also been proposed for the in vivo measurement and monitoring of other parameters in a patient's blood. A particularly effective system is the Paratrend 7.TM. system developed by Biomedical Sensors Ltd., which includes a multiparameter catheter comprising sensors for the determination of pO.sub.2, pCO.sub.2, pH and temperature.
The oxygen sensor used in the multi-parameter catheter may be an electrochemical sensor similar to that used in the commercially available Continucath 1000.TM., but with certain improvements such as those described and claimed in U.S. Pat. No. 5,262,037 or patent application Ser. No. 08/095232.
While the determination of blood pO.sub.2, for conditions where ventilation support is indicated, is performed effectively by the Continucath 1000.TM. and Paratrend 7.TM. systems inserted in a patient's artery, there are some conditions where an alternative or additional site of measurement, particularly for measuring regional perfusion, is indicated. Thus, it has been postulated that urine oxygen may track kidney oxygen tension and some studies have been performed, with inconclusive results. Also, it is theorized that bladder perfusion behaves similarly to organs like the gastrointestinal tract, skin and kidney, in that blood flow is diverted from the bladder to more critical organs during shock. Bladder pO.sub.2, more strictly bladder epithelial pO.sub.2, indicated hereinafter as pbO.sub.2 responds more quickly to hemodynamic variations than urine pO.sub.2 as a relatively non-invasive early indicator of poor organ perfusion with a view to provide an early warning, leading to prevention or earlier treatment, of multiple organ failure.
Surprisingly it has now been found from rat models that pbO.sub.2 changes rapidly in relation to the circulatory status of the animal and provides a reliable indication of concurrent changes in systemic blood pressure (BP), aortic (ABF) and renal (RBF) blood flow.